Commercial development has led to advances in the manufacture and use of lubricants that are miscible with HFC-134a refrigerant (1,1,1,2-tetrafluoroethane) and other fluorinated refrigerants. For example, U.S. Pat. No. 4,916,914 proposes certain lubricants, for compression refrigeration systems which utilize R134a. HFC-134a is the refrigerant of choice since the Montreal Accords restrict the production of refrigerant CFC-12 (R-12) by the year 1990 due to the refrigerants' untoward effect of depleting atmospheric ozone.
H. H. Kruse et al in "Fundamentals of Lubrication in Refrigeration Systems and Heat Pumps" which is incorporated herein by reference, pages 763-783, Ashrae Transactions Vol. 90 part 2B (1984), discusses systems of the type with which the present invention finds use. Research has developed various esters in combination with other fluids (or lubricants), such as other esters, mineral oils, polyglycols and alkylbenzenes, to be used as lubricant fluids in combination with the fluorinated refrigerants. Such esters are made by reacting an alcohol with acid. In the case of lubricants, the alcohol is a relatively high molecular weight molecule (compared to ethanol) and the acid generally ranges from C.sub.4 to C.sub.12. The most common esters derive from acids from C.sub.5 to C.sub.10.
For example, U.S. Pat. Nos. 4,302,343, 4,751,012 and 4,851,144 all relate to lubricants including various blends of esters and polyether polyols which make long lasting lubricants. The '144 patent especially relates to the need for higher viscosity and miscibility. The present invention also addresses these issues. Additionally, U.S. Pat. No. 4,755,316 discloses a composition containing one or more polyether polyols for lubricating refrigeration compressors utilizing HFC-134a. However, the prior art does not provide satisfactory viscosity and lubricity at temperatures of use in combination with miscibility of lubricant fluids consisting of esters which do not include polyglycols, in the refrigerants to be designated at those same temperatures.
Various researchers have developed lubricant fluids having modified esters therein in an attempt to produce higher viscosity grades which are miscible in the refrigerant at working temperatures. For example, the British patent application GB2216541A discloses a working fluid/lubricant combination for use in mechanical vapor recompression type heat transfer devices wherein the fluid includes an ester in combination with the refrigerant, but not the ester of the present invention.
The present invention relates to improved lubricant fluids and their method of manufacture resulting in fluids having an excellent balance of miscibility and viscosity thereby making the fluids excellent components in compression refrigeration systems. The present invention provides esters having better lubricity than polyglycols, good chemical stability over wide ranges of temperature, better wearability, and a good combination of viscosity and miscibility characteristics.